1. Field of the Invention
The present invention relates to a directly-coupled high-temperature superconductor SQUID (Superconducting QUantum Interference Device) magnetic sensor in a single thin film structure having high sensitivity, which operates stably even in the environmental magnetic noise without the use of a magnetic shield or the like.
2. Description of the Related Art
The high-temperature superconductor SQUIDs are adequately sensitive magnetic sensors. However, directly-coupled high-temperature superconductor SQUID magnetic sensors in a single thin film structure using bi-crystal grain boundary junctions produce flux trapping/jumping when subjected to a magnetic field of tens to hundreds of nT, resulting in the unstable operation (for example, see Non-Patent Document 1). As such, when using the high-temperature superconductor SQUID magnetic sensors in the magnetic field for measurements or using the sensors in an environment with high magnetic field noise, it has been difficult to maintain the stable operation of the SQUID magnetic sensors without compromising the high sensitivity.
Non-Patent Document 1: Peter Selders, et al., “Reduction of 1/f-Noise in HTS-SQUIDs by Artificial Defects”, IEEE Trans. Appl. Supercond., vol. 9, no. 2, pp. 2967-2970, 1999